Conventional plastic ball grid array ("PBGA") packages are used in a variety of semiconductor applications. Both micro-BGA and PBGA packages are currently available. Conventional micro-BGA packages are chip-scale packages. As their name suggests, conventional micro-BGA packages are significantly smaller than PBGA packages.
Conventional micro-BGA packages are formed on a tape substrate. Semiconductor dies are attached to the tape. Electrical connection is made between the dies and metal traces within the tape. The gaps between semiconductor dies are then filled with an adhesive encapsulant. The adhesive encapsulant aids in sealing and protecting the edges of the die. The tape is then cut between the dies, forming micro-BGA packages.
Conventional PBGA packages are significantly larger than conventional micro-BGA packages. Because of the difference in size, conventional PBGA packages are typically manufactured using very different processes and materials than micro-BGA packages. The conventional PBGA package includes a semiconductor die attached to a substrate. However, the substrate is similar to a printed circuit board. Typically, the substrate used is a BT (Bismaliemide Triazine) substrate. The substrate not only provides a relatively stiff surface to which the semiconductor die can be attached but also electrically couples the die to the solder balls. Consequently, the substrate includes conductive traces with insulating layers interspersed between the conductive traces.
Contacts on the semiconductor die are typically electrically coupled to the metallic traces in the substrate through wires bonded to a contact on the surface of the substrate. The semiconductor die is also typically covered in a molding compound, such as an epoxy. The molding compound aids in protecting the die from the environment and contributes to the robustness of the package. Solder balls on a side of the substrate opposite to the die can electrically connect the PBGA package to another circuit.
Typically, conventional PBGA packages are formed by attaching a number of dies to a long strip of substrate that is designed to accommodate the dies. The dies are then electrically coupled and molded to the substrate. After the PBGA packages are substantially formed, the substrate is cut to separate the conventional PBGA packages. The conventional PBGA packages may then be used in other circuits.
Although conventional PBGA packages are useful for many applications, the PBGA package may be prone to failure. For example, moisture may enter the substrate, and adversely affect the reliability of the PBGA package.
Accordingly, what is needed is a system and method for improving the reliability of the substrate in a PBGA package. The present invention addresses such a need.